Comparative Morphology Of Digestive System Of Cicadomorpha With Different Feeding Habits(Insecta: Hemiptera)

The Cicadomorpha is one of the most diverse lineages in hemipterans, including three superfamilies, Cicadoidea(cicadas), Membracoidea(leafhoppers and treehoppers), Cercopoidea(spittlebugs). They all suck the sap of their host plants by piercing-sucking mouthparts. In the long evolutionary history, different Cicadomorpha species have adapted with their own host plants(sucking the phloem sap or the xylem of woody plants or herbaceous plants), which might affect the morphology and ultrastructure of their internal organs. The gross morphology and ultrastructure of alimentary canals, salivary glands and Malpighian tubules in the representative species of the three lineages, Cicadoidea, Membracoidea and Cercopoidea, were investigated by the optical microscope and electron microscope, and then the associations between the differentiations and functions of these internal organs and their respective host plants were discussed, with the aims to offer more detailed information on coevolution. The main results are listed as follows:(1) Gross morphology and ultrastructure of alimentary canals and salivary glands of Membracoidea with different feeding habits.In the Membracoidea species feeding on herbaceous plants, the alimentary canals, especially the midgut loop, are relatively short and thick, and the salivary gland is relatively complex, with the principal gland consisting of the anterior lobe, lateral lobe and posterior lobe, while in the Membracoidea species feeding on woody plants, the alimentary canal, especially the midgut loop, are relatively long and thin, and the salivary gland is relatively simple, with the principal gland consisting of one or two parts of the anterior lobe, lateral lobe and posterior lobe. Ultrastructurally, the organs of digestive system of Atkinsoniella grahami and Kolla paulula both feeding on Setaria sp. are different from Dryodurgades lamellaris feeding on Salix babylonica. In Dryodurgades lamellaris, there are only a small number of mitochondria in the filter chamber, which are mainly distributed in the cytoplasm near the tunica intima; the midgut loop contains numerous secretory granules, and most of secretory granules are opaque, almost filling up the whole epithelial cells. In Kolla paulula, there are numerous mitochondria filling up filter chamber, uniformly, and the midgut loop has a small number of secretory granules, most of which are white. In the salivary gland of Atkinsoniella grahami, there are two kinds of secretory granules, i.e., white secretory granules and opaque secretory granules, meanwhile, the secretory granules in the salivary gland of Dryodurgades lamellaris are opaque, accompanied with numerous microorganism.(2) Gross morphology and ultrastructure of alimentary canal and salivary gland of Cercopoidea with different feeding habits.The gross morphology of digestive systems of different Cercopoidea species feeding on different hostplants is almost similar. Ultrastructurally, there are some differences between the species feeding different hostplants. Aphrophora costalis and Aphrophora oblique respectively feed on Salix babylonica and Artemisia argyi. The basilemma of the filter chamber in Aphrophora oblique is considerably invaginated, forming developed infoldings; the midgut loop contains a small number of mitochondria which scatter in the cytoplasm; the salivary gland is filled up with numerous secretory vesicle and flaplike rough endoplasmic reticulum. In Aphrophora costalis, basilemma of the filter chamber is slightly invaginated, forming short infoldings, and there are numerous mitochondria which mainly are distributed in cytoplasm near the infoldings and microvilli; the midgut loop contains a small number of mitochondria almost filling up the cytoplasm; the salivary gland contains almost no secretory vesicle, instead contains numerous rough endoplasmic reticula which are developed into enormous whorls of concentric cisternae.(3) Comparative morphology of the ultrastructure of Malpighian tubule between nymphs and adults in spittlebugs and cicadas.The ultrastructure of Malpighian tubule in nymphal spittlebugs and cicadas is significantly different from that in their respective adults. In nymphal spittlebugs, there are numerous secretory granules, secretory vesicles and developed rough endoplasmic reticula, and in nymphal cicadas, there are numerous secretory vesicles, which indicates that the Malpighian tubules have secretive functions in their nymphal stage. However, in the adult stage of spittlebugs and cicadas, no rough endoplasmic reticula are observed in the Malpighian tubules, and the secretory granules and/or secretory vesicles are dissolving or absent. The ultrastructural differentiation of Malpighian tubules might offer a plausible explanation to the different behaviors between nymphs and adults. The ultrastructures(e.g., secretory vesicles and/or secretory granules) of Malpighian tubules of nymphal spittlebugs and cicadas play an important role in secreting watery products. Thus, nymphs of spittlebugs and cicadas could make use of their copious watery excretion discharged by the anus, i.e., the spittlebug nymphs can be immersed in their watery excretion called foam for the whole nymphal stage, and the cicada nymphs can use watery excretion for cementing the burrow walls and removing mud from the legs.(4) Morphology and ultrastructure of bacteriomes of cicadas.The gross morphology and ultrastructure of bacteriomes in cicadas were firstly investigated in this study. Two pairs of bacteriomes are located at the coelom of the 5th and 6th abdominal segments, and they are independent organs which are linked with the spiracles by tracheas. The bacteriome units have two types of bacterial symbionts, i.e., free bacterial symbionts which are only observed in the cytoplasm of the peripheral bacteriocytes of bacteriome unit, and compact bacterial symbionts which are always in the cytoplasm of the central bacteriocytes. The two types of bacterial symbionts respectively occupying individual bacteriocytes probably weaken the direct competition and antagonistic interactions. The adjacency of bacteriomes to the ovaries in females probably can facilitate the transfer of symbionts from the bacteriocytes to the ovaries in vivo in the early embryo development stages, e.g., keeping the symbionts from being degraded in the hemolymph in the transfer.This investigation suggests that:(1) the morphology and ultrastructure of the alimentary canal and salivary gland are much associated with the hostplants, which may possibly be effected by the different nutrient contained in the hostplant saps;(2) the behaviors of nymphs and adults in spittlebugs and cicadas are much associated with the ultrastructure of their respective Malpighian tubules, and the Malpighian tubules have both secretive and excretive functions in the nymphal stage, and in the adult stage the Malpighian tubules possess only excretive function;(3) the bacteriomes are independent organs, in which different symbionts are harbored in different bacteriocytes; the adjacency of bacteriomes to the ovaries in females probably can facilitate the transfer of symbionts from the bacteriocytes to the ovaries in vivo in the early embryo development stages; the secretory products of bacterial symbionts in the bacteriomes might be transferred across the membrane, and be released into the hemolymph.